Apt anagram of "aye" (3)
I believe the answer is:
yea
'apt anagram of aye' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for yea that I've seen before include "Aye; aye (anag.)" , "Affirmative in the British Parliament" , "Yes (archaic)" , "Approval" , "Certainly (archaic)" .)